Chemistry Gases MDCAT 2010
PMDC Verified Question 64 of 65
Which one of the following expressions represent the Avogadro law?
A
V= RnT/P (When T and n are constant)
B
V= RnT/P (When T and P are constant)
C
V= RnT/P (When P and n are constant)
D
V= RP/nT (When T, P and n are constant)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: V= RnT/P (When T and P are constant)
Concept:

Avogadro's Law states that equal volumes of all ideal gases at the same temperature and pressure contain the same number of molecules (or moles).

Formula:

$$ V \propto n \quad \text{(at constant T and P)} $$

Solution:

  • Starting with the ideal gas equation: \( PV = nRT \)


  • Rearranging for Volume (V): \( V = \frac{nRT}{P} \)


  • For \( V \) to be directly proportional to \( n \) (Avogadro's Law), the terms \( R \), \( T \), and \( P \) must all be constant.


  • Therefore, the expression \( V = \frac{RnT}{P} \) represents Avogadro's law strictly when Temperature (T) and Pressure (P) are constant.


Why other options are incorrect:

  • Option A: If \( n \) is constant, the relationship explores Boyle's or Charles's law, not Avogadro's.
  • Option C: If \( n \) is constant, it is not Avogadro's law.
  • Option D: The formula itself is mathematically incorrect derived from \( PV=nRT \).

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